Pneumatic motorcycle tire for improved cornering and straight running stability

ABSTRACT

A pneumatic motorcycle tire provided with a spiral belt and a pair of axially spaced reinforcing layers radially inside of the belt to improve the cornering stability and straight running stability of a motorcycle.

This is a divisional of application Ser. No. 08/251,970, filed on Jun.1, 1994, now U.S. Pat. No. 5,482,102 the entire contents of which arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a pneumatic motorcycle tire, which isprovided with a spiral belt and a pair of axially spaced reinforcinglayers radially inside of the belt to improve the cornering stabilityand straight running stability.

2. Description of the Background Art

Recently, as the expressway network has become widely developed, thedemand for high speed running of motorcyclesis increasing.

The radial tire for such motorcycles was hitherto designed andmanufactured on the basis of a radial tire for a four-wheel vehicle, andit could not follow up the cornering performance and straight runningperformance which are characteristic of a motorcycle. In particular,high speed steering stability was inferior.

As a reason therefor, a conventional belt 1 for reinforcing the treadportion was disposed in the same way as in the four-wheel vehicle, withinclining its cords (b) at 13 to 30 degrees to the tire equator as shownin FIG. 7(A). Such belt (a) with the inclined cords (b) was, as shown inFIG. 7(B), formed by cutting a sheet (d) of tire fabric having cords (b)extending in the longitudinal direction thereof, by the same angle asthe inclination angle (alpha) of the cords (d) of the belt (a), to forma parallelopiped pieces (e), and linking them in a series, with abuttingthe edges (f) of the pieces (e). Thus, the formed belt (a) has abuttingparts (f) passing obliquely to the tire axial direction. As the abuttingpart does not contact with the ground simultaneously during running, thehandling becomes unstable, and the straight running performance isimpeded. Further, during cornering, handling is also unstable. Theseoccur particularly during high speed running.

In order to solve part of these problems, a tire having a belt formed byspirally winding a narrow and long ribbon-shaped strip has beenproposed. In this tire, as shown in FIG. 8, one ribbon-shaped strip (g)is wound continuously from one end to the other end of the belt (h).Therefore, the belt (h) provides a uniform rigidity or a constantreinforcement for both the tread central region (j) and shoulder region(k).

On the other hand, as a motorcycle is inclined largely during corneringunlike the four-wheel vehicles, a larger camber thrust must be generatedduring cornering.

The above-mentioned tire having the uniformly reinforced tread portioncan be improved in the straight running performance, but the treadportion is liable to collapse by the lateral force applied duringcornering, and the cornering performance is deteriorated. Thisphenomenon is particularly notable when the belt is formed by spirallywinding a ribbon-shaped strip. As the ribbon-shaped strip is woundspirally, the cords in the ribbon-shaped strip are wound at nearly 0degrees to the tire equator. As a result, the resistance of the carcassand belt against lateral force is poor.

In order to increase the resistance against lateral force, if areinforcing cord layer (m) made of a sheet of conventional tire fabricis disposed over the entire width of the belt (g) as shown in FIG. 9,the rigidity of the tread shoulder region is improved, and the camberthrust occurs and becomes a large value early when the motorcycle makesa turn, whereby the cornering performance can be improved.

However, the ground contact and steering stability during straightrunning are deteriorated since the tread central region (j) is increasedin the bending rigidity.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a pneumaticmotorcycle tire which is improved in both the cornering stability andstraight running stability.

According to one aspect of the present invention, a pneumatic motorcycletire comprises

a tread portion with axial edges, the tread portion curved so that themaximum cross sectional width of the tire lies between the tread edges,

a pair of axially spaced bead portions,

a pair of sidewall portions extending between the tread edges and thebead portions,

a pair of bead cores one disposed in each bead portion,

a carcass having a main portion extending between the bead portionsthrough the tread portion and sidewall portions, and a pair of turned upportions each turned up around each bead core,

a belt disposed radially outside the carcass and inside the treadportion, the belt formed by spirally winding a ribbon-shaped strip ofrubber in which a single cord or a plurality of parallel cords areembedded along the longitudinal direction thereof, at a small angle tothe tire equator,

a pair of reinforcing cord layers disposed radially inside of the belt,

each reinforcing cord layer extending from a point P1 in the treadportion into the sidewall portion over the belt edge along the outersurface of the carcass,

the point P1 spaced apart from the tire equator such that, when a normalline is drawn normal to the tread surface through the point P1, thedistance measured along the tread surface from the tire equator to thenormal line is in the range of from 0.2 to 0.3 times the tread surfacewidth WT measured along the tread surface from one tread edge to theother tread edge,

each reinforcing cord layer comprising a ply of parallel organic fibercords inclined at an angle of 20 to 70 degrees to the tire equator,

the ply rubberized with a topping rubber having a 100% modulus of 25 to55 kgf/cm².

Accordingly, as the belt is formed by spirally winding a single cord ora plurality of cords at a small inclination angle to the tire equator,the belt is continuous in the circumferential direction incontradistinction to the conventional cut ply belt shown in FIG. 7(B).Therefore, the running stability and ride comfort are improved.

Since the reinforcing cord layer extends from the middle point P1between the tire equator and tread edge into the sidewall portion, thetread shoulder region is reinforced greatly than the tread central part.Therefore, the collapse of the tread portion caused during cornering bygiving a bank angle to the motorcycle can be prevented. Further, the lowor medium speed cornering becomes stable since the rigidity of the treadshoulder region is increased. Also, the high speed cornering becomesstable since the belt cord is continuous in the circumferentialdirection.

Further, since the reinforcing cord layers are disposed radially insideof the belt, the straight running is stable and the straight runningperformance is not lowered, although the cords are not parallel to thetire equator.

Furthermore, since the reinforcing cord layer is formed independentlyfrom the belt and carcass, the tread rigidity can be adjusted easily, ascompared with such a tread portion reinforced with a multi-ply belt oran extension of the carcass turned up portion.

If the distance of the point P1 is less than 0.2 times the tread widthWT, the width of the overlap of the reinforcing cord layer with the beltis excessively increased, and the ride comfort and ground contactperformance during straight running are deteriorated. Further, the tireweight, fuel consumption, running noise increase and production costincrease.

If the distance is more than 0.3 times WT, the running stability becomeslowered during slow cornering with a small bank angle since thereinforcing cord layer is located away from the ground contactingregion. If the 100% modulus of the topping rubber for the reinforcingcords is less than 25 kgf/cm², the lateral rigidity from the treadshoulder region to the sidewall portion becomes insufficient, and thecamber thrust also becomes insufficient for the camber angle. And thetime lag for the generation of camber thrust becomes large, therebyresulting in unsteady of the machine, and the high speed steeringperformance is deteriorated. To the contrary, if the 100% modulus ismore than 55 kgf/cm², the ride comfort during straight running isgreatly deteriorated.

In the present invention, thus, the cornering performance and straightrunning performance are improved.

Other objects and further scope of applicability of the presentinvention will become apparent from the described description givenhereinafter. It should be understood, however, that the detaileddescription and specific examples, while indicating preferredembodiments of the invention, are given by way of illustration only,since various changes and modifications within the spirit and scope ofthe invention will become apparent to those skilled in the art from thisdetailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described in detail inconjunction with the drawings.

FIG. 1 is a cross sectional view showing an embodiment of the presentinvention;

FIG. 2 is a cross sectional view showing another embodiment of thepresent invention;

FIG. 3 is a cross sectional view showing still another embodiment of thepresent invention;

FIG. 4 is a developed plan view of the belt and the reinforcing cordlayers showing an example of the cord arrangement;

FIG. 5 is an enlarged schematic perspective view of an example of theribbon-shaped strip;

FIG. 6 is a schematic sectional view explaining an example of the spiralwinding of the ribbon-shaped strip;

FIG. 7(A) and (B) are diagrams showing conventional belts; and

FIGS. 8 and 9 are cross sectional views each showing a prior art tire.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIGS. 1-3, a pneumatic motorcycle tire 1 comprises a tread portion 2with a tread surface 2A and tread edges E1 and E2, a pair of axiallyspaced bead portions 4 with a bead core 5 therein, and a pair ofsidewall portions 3 extending between the tread edges and bead portions.Further, the tire 1 comprises a carcass 6, a belt 7 and a pair of beadapexes 8.

In the tire meridian section, the tread surface 2A between the treadedges E1 and E2 is provided with a curved profile formed by a circulararc, and the maximum tire section width lies between the tread edges E1and E2.

The carcass 6 comprises at least one ply, in FIGS. 1, 2 and 3 only oneply, having a main portion 6a extending between the bead portions 4through the tread portion 2 and sidewall portions 3, and a pair ofturned up portions 6b each turned up around each of the bead cores 5from the axially inside to outside of the tire. The or each carcass plyis made of cords arranged radially at an angle in the range of from 70to 90 degrees with respect to the tire equator C to have a radial orsemiradial ply construction. For the carcass cords, organic fiber cords,e.g. nylon, rayon, polyester, aromatic polyamide and the like are used.

The radially outer end of the carcass turned up portion 6b is extendedradially outwardly from the bead portion 4 to a position near the beltedge in FIGS. 1 and 3 or a position about 50% of the tread edge heightHE in FIG. 2.

Each of the bead apexes 8 is disposed in each bead portion 4 between thecarcass main portion 6a and each turned up portion 6b and radiallyoutside of the bead core 5. The bead apex 8 is made of rubber having aShore A hardness in a range of 40 to 95 degrees and a triangular shapetapering radially outward from the bead core. The upper end of the beadapex is extended near the tread edge.

The belt 7 is disposed radially outside the carcass 6 and inside thetread portion 2.

The belt 7 consists of one ply of a single cord or a plurality of cordswound spirally around the carcass 6 at a small angle of not more than 5degrees with respect to the tire equator C.

For such belt cords 14, organic fiber cords, e.g. nylon, polyester,aromatic polyamide and the like or steel cords can be used.

Preferably, the width WB of the belt 7 is in the range of 0.85 to 0.95times the tread width WT. Here, the belt width WB is measured along theouter surface of the belt, and the tread width WT is measured betweenthe edges F1 and F2 along the tread surface.

If less than 0.85 times, the rigidity of the tread edge portion isdecreased, and the steering stability is impaired during cornering bylargely inclining the machine.

If mope than 0.95 times, the rubber thickness from the belt edge to thesidewall surface becomes decreased, and the upper sidewall portion isliable to crack with decreasing the durability.

The above-mentioned belt ply is formed by spirally winding a longcontinuous narrow-width ribbon-shaped strip 10.

The ribbon-shaped strip 10 is, as shown in FIG. 5, formed such that onebelt cord or a plurality of parallel belt cords, in this example twocords 14, are embedded in a topping rubber 15.

Such a ribbon-shaped strip 10 is wound continuously from one belt edgeF1 near one tread edge E1 to the other belt edge F2 near the other treadedge E2, across the tire equator C.

In the winding operation of the ribbon-shaped strip 10, as shown in FIG.B, the confronting side edges 10a and 10a of the strip 10 can beoverlapped to prevent loosening.

In all the embodiments shown in FIGS. 1, 2 and 3, the belt 7 is formedof a single ply 7a, but the belt may be of two or more plies. In otherwords, the ribbon-shaped strip 10 may be wound double or more.

According to the present invention, a pair of axially spaced reinforcingcord layers 9 are disposed radially inside of the belt 7 and outside ofthe carcass 6.

Each reinforcing cord layer 9 is made of one ply of rubberized parallelorganic fiber cords 16, e.g. nylon, rayon, aromatic polyamide and thelike, laid at an angle of 20 to 70 degrees to the tire equator C. Withrespect to the tire equator, the cords of one layer are inclinedreversely to the cords of the other layer.

For the topping rubber for the reinforcing cords, a rubber compositionhaving a 100% modulus of 25 to 55 kgf/cm² is used.

Each of the reinforcing cord layers 9 extends along the outer surface ofthe carcass 6, axially outwardly from a point P1 in the middle betweenthe tire equator and tread edge, over the belt edge F1 and F2, and thenradially inwardly toward the sidewall portion.

The point P1 is spaced apart from the tire equator C as follows. When astraight line N is drawn normal to the tread surface 2A through thepoint P1, the distance measured along the tread surface 2A from the tireequator C to the normal line N (point 0) is in the range of from 0.2 to0.3 times the above-mentioned tread width WT. Preferably, the distanceis 0.25 times the tread width WT.

When a motorcycle is inclined by giving a camber angle in order tochange the running direction, if a large time lag occurs until thegeneration of camber thrust, the driver feels as difficult to run in theintended course, and increases the camber angle for further chamberthrust. However, after a certain time lag, an excessive camber thrustoccurs to cause an over-steering. It is therefore, important to shortenthe time lag. Thus, such a time lag results in unsteady feelings to thedriver in case of motorcycles.

Such a time lag can be shortened by increasing the lateral rigidity ofthe tire, especially ranging from the tread shoulder region 12 to thesidewall portion 3.

For straight running, however, it is necessary to decrease the rigidityof the tread center region 11 since the central region contacts with theground during straight running, and it is important to improve theground contact for maneuverability and wear resistance.

According to the present invention, the reinforcing cord layers 9 rangefrom the tread shoulder region 12 to the sidewall region, and the angleof the reinforcing cords is crosswise to that of the carcass cords.Therefore, the lateral rigidity of the tire when a camber angle is giventhereto, is increased to shorten the time lag, and the steeringstability is improved.

Further, the reinforcements in the central region 11 are only the beltcords 14 laid substantially parallel to the circumferential directionand carcass cords laid generally in the axial direction. Accordingly,this region is low in bending rigidity. As a result, vibrations duringrunning due to road undulations and slip between the road surface andtire are effectively decreased, and the tread wear life is prolonged.Further, running noise and harshness are effectively alleviated.

The other end P2 of each reinforcing cord layer 9 is positioned in therange R1 of from 0.1 to 1.0 times the tread edge height HE which is theradial distance from the baseline L to the tread edge E1 and E2.

In FIG. 1, the end P2 is positioned at a height slightly lower than thetread edge height HE so that the layers 9 reinforce only the treadshoulder region 12.

In FIG. 2, the end P2 is positioned at a height H2 slightly higher than10% of the tread edge height HE so that the layers 9 reinforce both thetread shoulder region 12 and sidewall portion 3.

By covering the edge of the carcass turned up portion 6b within thereinforcing cord layer 9, a carcass ply edge separation can be preventedto improve the durability.

In FIGS. 1 and 2, in the sidewall portion 3 and bead portion 4, thereinforcing cord layer 9 is disposed axially outside the carcass turnedup portion 6b and not turned up around the bead core 6.

In FIG. 3, however, the reinforcing cord layer 9A is extended to thebead base and turned up around the bead core 5, to further extend alongthe axially inside of the carcass main portion 6a. In this case, alsothe end P3 thereof is positioned at a height H3 in the same range R2 offrom 0.1 to 1.0 times the tread edge height HE. In this example, the endP3 is positioned slightly lower than the tread edge height HE.Accordingly, the sidewall portions 3 are effectively reinforced, and thehigh speed cornering performance and the engaging force with the rim areeffectively improved.

Test tires having a tire size of 190/50 R17 were prepared and tested forthe following performances. The specifications of the test tires andtest results are shown in Table 1.

1) High speed straight running stability and High speed corneringstability

Test tires were installed in a motorcycle, and the motorcycle was run ona test road at a speed of 260 km/h on a straight course and at 220 km/hon a 400 meter radius curved course. The performance was evaluated bythe feeling of the test driver, and expressed by an index based on theprior art tire being 100. The greater the index, the better theperformance.

2) Running stability during slow and Middle speed cornering

Running a curved road at a speed of less than 100 km/h, the test tireswere tested same as in 1). The result was expressed by an index based onthe prior art tire being 100. The greater the index, the better theperformance.

3) Durability

Each test tire, which was inflated to 2.5 kgf/cm² and loaded with 130%of the maximum load specified in Japanese Industrial Standard, was runat a speed of 50 km/h, using a testing drum machine. The result wasexpressed by an index based on the tire which was successful in 15000kilometer running without damage as index 100.

4) Vibration ride comfort

The ride comfort was evaluated by the feeling of the test driver throughthe test 1), and expressed by an index based on the prior art tire being100. The greater the index, the better the performance.

5) Tire weight

The tire weight was measured, and expressed by an index based on theprior art tire being 100. The greater the index, the heavier the tireweight.

Through the tests, It was confirmed that the example tires wereexcellent in both high speed and slow speed cornering performances ascompared with the prior art tire and comparative example tires. Further,the high speed straight running performance was not inferior as comparedwith the comparative example tires.

As explained above, in the pneumatic motorcycle tire of the presentinvention, the belt is formed by spirally winding a ribbon-shaped strip,and a pair of axially spaced reinforcing cord layers are provided inwardof the belt to reinforce the tread shoulder region. Therefore, thecornering performance during both high speed and slow speed running canbe improved without lowering the high speed straight runningperformance.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

                                      TABLE 1                                     __________________________________________________________________________           Tire                                                                          Ex. 1                                                                             Ex. 2                                                                             Ex. 3                                                                             Ex. 4                                                                             Ex. 5                                                                             Ex. 6                                                                             Ex. 7                                                                             Prior                                                                             Ref. 1                                                                            Ref. 2                                                                            Ref. 3                                                                            Ref.                                                                              Ref.                                                                              Ref. 6                    Tire construction                                                             FIG. 2                                                                            FIG. 2                                                                            FIG. 2                                                                            FIG. 2                                                                            FIG. 2                                                                            FIG. 3                                                                            FIG. 3                                                                            FIG. 8                                                                            FIG. 9                                                                            FIG. 2                                                                            FIG. 2                                                                            FIG.                                                                              FIG.                                                                              FIG.               __________________________________________________________________________                                                               3                  Carcass                                                                       No. of ply                                                                           1                                                                      Cord material                                                                        nylon                                                                  Cord denier                                                                          2/1260d (51 ends/5 cm)                                                 (Cord count)                                                                  Cord angle                                                                           88 degrees to Tire equator                                             Turnup height/                                                                       0.65                                                                              0.65                                                                              0.65                                                                              0.4 0.4 0.4 0.4 0.65                                                                              0.65                                                                              0.65                                                                              0.35                                                                              0.35                                                                              0.35                                                                              0.35               HE                                                                            Belt                                                                          Construction                                                                         Spirally wound strip                                                   No. of ply                                                                           1   1       1               1   1   1   1   1   1   1                  Width ratio                                                                          0.85                                                                              0.88    0.95            0.88                                                                              0.88                                                                              0.88                                                                              0.80                                                                              1.0 0.88                                                                              0.88               WB/WT                                                                         Cord material                                                                        aramid                                                                            aramid  aramid          aramid                                     Cord denier                                                                          3/1500d                                                                           3/1500d 2/1500d         3/1500d                                    No. of cord                                                                          2   2       2               2                                          per a strip                                                                   Cord angle to                                                                        0   0   5   0   0   0   0   0   0   0   0   0   0   0                  equator (deg)                                                                 100% modulus                                                                         25  55  35  40  40  40  40  35  35  35  35  35  35  35                 of topping                                                                    rubber                                                                        (kgf/sq. cm)                                                                  Filler                             non                                        Cord material                                                                        nylon                           nylon                                  Cord denier                                                                          2/1260d                         2/1260d                                Cord count                                                                           28                              28                                     (/5 cm)                                                                       Cord angle to                                                                        20  70  45  45  45  45  45      40  15  75  40  45  45                 equator (deg)                                                                 100% modulus                                                                         25  55  35  40  40  35  35      35  58  35  22  35  35                 of topping                                                                    rubber                                                                        (kgf/sq. cm)                                                                  Position                                                                             0.2 0.3 0.75                                                                              0.25                                                                              0.25                                                                              0.25                                                                              0.25    *1  0.4 0.1 0.3 0.2 0.3                P1/WT                                                                         Position                                                                             1.0 0.1 1.0 0.3 0.3 0.1 1.0     1.0 0.5 1.0 1.0 0.1 1.1                (P2 or P3)/HE                                                                 Test Results                                                                  Running                                                                       stability                                                                     High   115 115 110 120 120 115 115 100 90  110 90  100 115 115                speed straight                                                                High   115 125 115 125 125 120 125 100 105 100 95  100 105 115                speed cornering                                                               Low/Mid                                                                              115 115 115 120 120 115 115 100 105 105 95  100 105 115                speed cornering                                                               Durability                                                                           100 100 100 100 100 100 100 100 100 100 100 *2)90                                                                             100 100                Vibration ride                                                                       100 100 100 100 100 100 100 100 90  95  95  100 100 95                 comfort                                                                       Tire weight                                                                          106 107 105 106 106 107 108 100 108 105 107 105 105 110                __________________________________________________________________________     *1) a continuous one piece filler                                             *2) a belt edge separation occurred during 13,500 km running             

I claim:
 1. A pneumatic motorcycle tire comprisinga tread portion withaxial edges, said tread portion curved so that the maximumcross-sectional width of the tire lies between the tread edges, a pairof axially spaced bead portions, a pair of sidewall portions extendingbetween the tread edges and the bead portions, a pair of bead cores, onedisposed in each bead portion, a radial carcass comprising at least oneply of cords having a main portion extending between the bead portionsand a pair of turned up portions each turned up around one of said beadcores, the cords of the carcass having an angle of from 70 to 90 degreeswith respect to the tire equator, a belt disposed radially outside thecarcass and inside the tread portion, said belt consisting of a singleply formed by spirally winding a ribbon-shaped strip of rubber in whichat least one cord is embedded along the longitudinal direction thereof,at an angle to the tire equator, a pair of axially spaced reinforcingcord layers disposed radially inside of the belt and outside of thecarcass, each reinforcing cord layer extending from a point (P1) in thetread portion on each side of the tire equator towards the sidewallportion beyond the belt edge, said point (P1) being spaced apart fromthe tire equator such that, when a straight line is drawn normal to thetread surface through the point, the distance measured along the treadsurface from the tire equator to the normal line is in a range of from0.2 to 0.3 times the tread surface width measured along a tread surfacefrom one tread edge to the other tread edge, with respect to the tireequator, the cords of one of the reinforcing cord layers are inclinedreversely to the cords of the other reinforcing cord layer, eachreinforcing cord layer consisting of a single ply of parallel organicfiber cords inclined at an angle of 20 to 70 degrees to the tire equatorto cross the carcass cords, said ply of each said reinforcing cord layerbeing rubberized with a topping rubber having a 100% modulus of 25 to 55kgf/sq.cm, each reinforcing cord layer being turned up around the beadcore from the axially outside to inside of the tire to have an axiallyouter portion and an axially inner turnup portion extending radiallyoutwardly from a base of the bead portion along the axially inside ofthe carcass main portion, and said turnup portion terminated at a heightin the range of from 0.1 to 1.0 times the height of a tread edge, eachmeasured from the base of the bead portion.
 2. The tire according toclaim 1, wherein said belt has a width in a range of 0.85 to 0.95 timesa tread surface width.
 3. The tire according to claim 1, wherein saidheight of the turnup portion is in the range of from 0.1 to 0.3 timesthe height of the tread edge.